ECE/CS 250: MIPS assembly clinic

Materials

Screenshot	Source file(s)	Description
pic1	prog1.c, prog1.s	Side-by-side C and Assembly for a simple loop
pic2	-	Running the simple C program
pic3	ternary.txt	Explaining the ternary operator (c?a:b)
pic4	prog1.s in QtSpim	QtSpim interface
pic5	-	Output of prog1 in QtSpim
pic6	-	Explaining I-type instruction encoding
pic7	prog2.c, prog2.s	Side-by-side C and Assembly for some linked list code
pic8	malloc.s	Explaining malloc as if it's just a function that does an sbrk syscall (don't use this code directly; it's silly!)

Timeline

• 0:00:00 - Look at pic1. Go through C code on left.
• 0:01:30 - Look at pic2; we're running the C program.
• 0:02:00 - Look at pic1, we build the asm code on the right.
• 0:13:00 - Look at the quick-ref sheet here. I also make brief reference to this as an alternative. Later, when I refer to looking up syscalls online, Google gave me this link.
• 0:18:00 - Look at pic3. As an aside here, I explain the ternary operator (used in C, Java, and as a notation on the MIPS quick-ref sheet for slt).
• 0:19:05 - Back to the quick-ref from 0:13:00 to glance at slt
• 0:19:10 - Back to pic1
• 0:30:00 - The code mentioned is lines 44-46 on pic1; lines 39-42 and 47+ come later
• 0:31:00 - I go back and add the .globl directives (lines 3,37 in pic1)
• 0:32:00 - We start looking at QtSpim. Run it to follow along. See pic4 for reference, which is annotated.
• 0:34:24 - The button I describe as bad is the first toolbar button, the regular 'load' button. You want the second button, 'Reinitialize and load'. See pic4 annotations.
• 0:37:00 - I'm describing the loader, annotated in pic4.
• 0:40:15 - See pic5 for the console when it ran.
• 0:43:00 - Around here I navigate around QtSpim, including the memory viewer.
• 0:48:40 - Back to pic1 as we update the code. Lines 39-42 and 47+ don't exist yet.
• 0:50:15 - I'm talking about the jr on line 57.
• 0:52:50 - We start talking about creating lines 39-42 and 51-54.
• 0:54:42 - "Step 1" is line 40, then I do the stores on lines 41-42
• 0:58:30 - We copy/paste from 40-42 to 52-54, move the add to the bottom, flip the sign on it, and change the stores to loads. Boom: restore-from-stack code.
• 1:01:40 - Back to QtSpim (run it live or see pic4). You'll hear me right-click an instruction an 'Set breakpoint'.
• 1:10:45 - See pic6 as I explain how to we encode lw as an I-type binary instruction.
• 1:17:00 - Back to pic1 as I answer a few questions about the code.
• 1:18:30 - Time for pic7! Linked list example. I type the C code on the left first.
• 1:25:25 - See pic8 for fake 'malloc' side-example.
• 1:29:25 - Back to pic7.
• 1:35:00 - I change the C program (and thus our goal) to sum two pieces of the struct into a variable q instead of printing.
• 1:44:55 - I start writing the makeanode C code on the left.
• 1:45:55 - I start writing the equivalent assembly on the right.
• 1:50:00 - We start writing line 43, but line 42 doesn't exist yet.
• 1:51:35 - Now I go back and realize the need for line 42 and write that. We soon finish the function, but note the function is silly: we're missing a way to return the pointer and actually returning from the function (jr $ra)
• 2:01:42 - I say "Goodbye video, hopefully you encode without dying." The video immediately dies while encoding. :-(